Studies characterizing malarial antigens and the humoral response of mice to Plasmodium yoelii were continued. During this year we produced, cloned, and cryopreserved 137 anti-P. yoelli hybridoma cell lines. These can now be used to identify biologically important antigens. In addition, a series of experiments were undertaken to determine 1) the number and molecular size of malarial immunogens that stimulate Ab production during malaria, 2) the requirement for T cells in antimalaria Ab production, and 3) the kinetics of Ab induction by non-species specific (crossreactive) Plasmodial Ags. Results from these studies demonstrate that P. yoelii parasites have at least 33 protein immunogens that the Ags require T cells for Ab production, i.e. P. yoelii lacks T-independent Ags, and that antigenic determinants (i.e. epitopes) common to related malaria parasites may be present on immunogens of different molecular weights. Experiments were also initiated this year to determine if a correlation exists between the kinetics of Ab response to stimulatory malarial Ags and the genetics of host resistance to rodent malaria.